Synchronous motor starting control



April 18, 1950 E. M. DAUGERT 2,504,812

SYNCHRONOUS MOTOR STARTING CONTROL Filed Jan. 29, 1948 l N V E N TO R5777! 1 0,-,- M page/f,

v2, 5" z? KTMW ATTORNEY Patented Apr. 18, 1950 SYNCHRONOUS MOTORSTARTING CONTROL Emilian M. Daugcrt, Upper Darby, Pa assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa, a corporation ofPennsylvania Application January 29, 1948, Serial No. 5,076

5 Claims.

My invention relates to electric systems of control for automaticallstarting, accelerating, synchronizing and, in the event of pull-cut,resynchronizing synchronous motors.

It is Well known and usual practice to start a synchronous motor as aninduction motor on the damper winding and at the balancing speed, themaximum induction motor speed, to transfer the motor from inductionmotor operation to synchronous motor operation by exciting the fieldwinding. Various au omatice control systems are well known in the artfor this general purpose. With most of such automatic starting controlsystems, no provision is made to eliminate the undesirable surge that isoccasioned when the field excitation is applied and such application ofthe field excitation takes place, as is usually the case, at an instantwhen the pole pieces are not in the most favorable position withreference to the rotating magnetic flux produced by the alternatingcurrent in the armature windings of the motor.

I am aware that others have proposed to control the instant ofexcitation of the synchronous motor field winding so as to obtain amaximum pull-in torque, and, in consequence, also a minimum of theelectrical surge of current in the armature winding and also a minimumof mechanieal shock to the motor and the mechanical load that is usuallycoupled to the motor.

Such prior art devices, however, were not capable of accurately, withina very few degrees, selecting the correct angular position of the polepieces with reference to the rotating flux and the structure of thearmature Winding.

It is, therefore, a broad object of my invention to provide forefiectively controlling the time of excitation of the field winding withreference to the rotating flux in the stator.

Another object of my invention is the accurate selection of the time ofenergization of the field winding to obtain maximum pull-in torque atsynchronization of the motor.

It is an important and somewhat more specific object of my invention toselect a particular point of a particular slip cycle of a synchronousmotor for the excitation of the field windings with direct current insuch a, manner as to provide a given polarity 0n given pairs ofalternate poles.

The objects hereinbefore stated are merely illustrative of the objectsof my invention. Many other objects and advantages will become moreapparent from a study of the following specification and the drawing inwhich the single figure is a diagrammatic showing of an embodiment of mysystem of control.

In the drawing, M designates the synchronous motor, the startingoperation of which is to be controlled. The energization of the motorfield winding F is controlled by the field contactor 23 and theconnection of the motor M to the alternating-current buses l, H] andHill is controlled by the line contactor it.

The field is provided with a discharge circuit including a dischargeresistor R1 and also the primary winding P of the transformer T. Thistransformer T through its secondar winding is interconnected with afrequency rela HI and a. pull-out relay P0. The frequenc relay HIcontrols the deenergization of a control relay SGI which in turncontrols the deenergization of another control relay SGZ similar to thecontrol relay SGl.

The characteristics of the frequency relay HI in conjunction with thecontrol relay SGI which has its coil shunted by an adjustable capacitor31, are so selected that the SGI relay will drop out at a selected percent slip of the synchronous motor. The second control rela SGZ alsobeing provided with capacitor timing and being subject to the drop outof control SGi drops out when a given point on the pole pieces 01 thefield winding of a given polarity holds a given position with referenceto a, point on th rotating wave of flux in the armature or primarystructure of the synchronous motor.

The 5G5 relay through a set-up relay 8G3 controls the field contactor 23and thus controls the excitation of the field winding F with directcurrent.

A more accurate understanding of my invention can very likely be had bya study of a typical starting cycle.

Assuming that the alternating-current buses i, it, and Hill areenergized and the source of direct current for the field is alsoavailable and it is desired to start the motor, then the attendantactuates the starting push button A, whereupon a circuit is establishedfrom bus I through conductor 2., the stop pushbutton 3, the start pushbutton the actuating coil 5 of the low voltage relay 3, contact l of theincomplete sequence time relay R, conductors 3 and 9 to thealternatingcurrent bus I ii. The low voltage relay t holds itself inthrough-contacts ll, and through-contacts l2 energizes conductor ,IE.Energization of conductors l6 and 5; thus provides alternatingcurrentpotential to the full-wave rectifier it to thus supply the buses ISandltwith direct-current energy. Energization of conductors it and 5% alsoestablishes a circuit for the line contactor 14 by the circuit fromconductor :8 through coil I3 and conductor is to conductor a. i of theline contactor it closes the contacts 21?, 28 and 5.9 to connect theprimary or armature wind ing of the motor to the alternatingecurrentbuses i, it, and its to thus start the motor on its damper winding as aninduction motor.

The energization of buses i8 and it with direct current establishes acircuit from conductor 58 through actuating coil 2B of the time limitrelay 22 and back contacts 25 on the field contactor 2'5 to the bus 59.The time limit contactor 22 almost instantly closes its contacts 25 tothus enere giZe the motor of the incomplete sequence timing relay R. I

While the motor M is accelerating as an induction motor, an alternatingcurrent induced in the field winding F traverses the discharge circuitof t e field which in lu s h esistor Bi a d 1- tacts til and thetransformer primary winding P. The transformer secondary winding Ssupplies energization for the frequency relay HI through the rectifier3i and the actuating coil 32. This sive direct-current pulsations aresufficiently long to cause the armature of the frequency relay to drop.

At the instant of starting, the current in coil 32 causes the HI relayto pick up to close the contacts 33 and 38. established from thedirect-current bus I 8 through contact 33, actuating coil 34, backcontact 35 of the time limit relay 36 to the bus l9. The closure of thecontact 33 establishes a, circuit from conductor or bus l8 throughcontacts 38, contacts 39 of the time limit relay 3%, actuatin coil in ofthe control relay SG2 to the bus [9. A capacitor 3'! shunts theactuating coil .34 and a similar capacitor ill shunts the actuating coiltil. These two re.- lays SGI and SGZ are similar in every respect,except that the adjustment of the capacitors may be and usually will bedifferent, since these relays will be required to operate in difierenttime intervals by the capacitor timing these capacitors provide.

The control relay SGI holds itself in throughcontacts 5 but the controlrelay SGE does not hold itself in directly by its own action but is heldin by the closure of both the contacts at on the control relay SGI andthe contacts 4? on the control relay 8G2. It is thus apparent that thesequence of operation must of necessity be, first, control relay SGlsecond, control relay SGZ.

Further, the control relay SGi holds itself in during vibration of thefrequency relay HI, by e s o he ca acitor t min the ca i r 3.? cQ nectcdin shunt el c t t /c03 nt l he c-pen ci ui time at on 3 ssuifi ien ly lns t0 c u e S tc .drep 91 Thec ntre rel y 8G2 has a similar capacitotimin ci b il i not direc ly su ect to n tim from the frequency relayfil 1d ca a tor '4 connected i shun elat on t coi t e a a i and o l Abethremai'n ergized until SGE drops to remove the by-pass contacts fromacross theirequency relay con tacts 351. It is thus apparent that thesequence of operation must of necessity be, first, SG! control relay andthen, second, SGZ control relay.

After operation of the control relay 5?}2, a Q11? By this operation acircuit is cuit is established from bus I8 through the back contacts 42of the pull-out relay PO, contacts 43, actuating coil M of the timelimit relay 36 to the bus The time limit relay 35 holds itself inthrough the closure of contacts 8% and its energized or actuatedposition is thus independent of the position of contacts 43.

The operation of the control elays 6G! and S012 causes the opening ofthe contacts 58 and 9. From this operation, it will be apparent that thecontrol relay having actuating coil 55, can only become energized whenboth contacts 43 and 555 are closed and contacts 56 are closed. At thetime the time limit relay 36 picks up to close contact contacts at andt9 are, 01 course, open. When the synchronous motor has attained verynear its balancing speed which may be from to 97% of the synchronousspeed, the frequency relay HI drops out to open contacts 33 to deem--ergize the coil as. The contacts as may even chattel once or twice, butthe adjustment of the capacitor 3? is such that the control relay SG!drops out at a selected per cent slip, as, for instance, a 3 slip. Whenthe frequency relay drops out, contacts 35 are also opened, and aninstant later, when contacts .45 open, the circuit for the actuatingcoil at of the control relay SGZ is interrupted. The adjustment ofcapacitor M with reference to the coil 49 is such that the control relay5G2 drops out with just the delay to close contacts 9 when a given pointon the pole piece of the synchronous motor of a given polarity holds agiven position with reference to a given point ,on the rotating wave offlux in the armature winding. From this, it is apparent that contact 4%)controls the energization of the actuating coil Si or" the set-up relaySCI-3 at a time When the rotating structure of the motor holds theabovementioned position with reference to the rotating field.

Operation of the set-up relay SGS closes the contacts 53, whereupon theactuating coil 52 of the field contactor 23 is energized. Operation ofthe field contactor causes the closing of contacts 54 and 55 and aninstant later the opening of contact Operation of the field contactoralso closes the contacts 56 to connect the actuating coil 57 of thepull-out relay to the secondar of the transformer T. The time constantsof both the field contactor 23 and the seteup relay 8G3 are extremelysmall, but can be accurately selected so that, when the field contactor23 eventually closes, the contacts 54 and 55 to energize the fieldwinding F with direct current, the energization will take place at aninstant when the pole pieces hold such a position With reference to therotating flux in the armature structure that the motor pulls in withmaximum pull-in torque.

Even with the most favorable synchronizing conditions, some currentsurge is produced in the held winding and it may happen that such currerg i the ev l 1 cf e u -ou e y sufficient to cause the opening ofcontacts '22 and the fleeing o c n acts nd 62- The ti de e th ime im trela 3.6 h we e i eu lc est o prevent o enin ef'contaets 59 un sin e e:nize e is complet O cou se af e t w eli on z t on is emele e. no rr ntil flew in the tin e 11 an in on e uen the c e s il main c osed.-

In the event of loss of synchronous operation o th me e by ea on .Of o eo 0 fo an other rea o tha m c use a p t. a cu 7t r n surge is P d c d nthe @11 of e u out relay and, in consequence, contacts 42 are opened todeenergize the time limit relay 3B which thus opens the contacts 59.Opening of contacts 5!] causes the opening of contacts 53 for thecircuit of the actuating coil of the field contactor and as a result,the direct-current excitation is removed from the field winding F. Themotor thus again operates as an induction motor to instantly establishthe conditions for resynchronization. The closure of contacts BI and 62again effects the energization of the control relays SG! and SG! in theorder named. An instant after the surge of current has ceased throughthe actuating coil 57, contacts 33 and 38 are closed by the frequencyrelay. The energizaticn of the control relays SGi and SGZ thereafter isindependent of the pull-out torque.

Synchronization, therefore, proceeds in exactly the same manner after apull-out, as during starting of the motor from rest.

While I have shown and described but a single embodiment of myinvention, I realize that others, particularly after having had thebenefit of the teachings of my invention, may devise similar systems ofcontrol for the same general purpose. I, therefore, do not wish to belimited to the details of the particular showing of my invention.

I claim as my invention:

1. In a synchronous motor starting control scheme of the type described,the combination of a synchronous motor having an armature, or primary,winding and a field winding, a plurality of terminal leads normallyenergized with alternating current, a pair of terminal leads normallyenergized with direct current, contactor for connecting the armaturewinding to the terminals energized with alternating current, a fieldcontactor for connecting the field winding to the terminals energizedwith direct current, and a control system for controlling the operationof the field contactor, said control system comprising an energizedcontrol circuit, a frequency relay interconnected with the field Windingto be energized with the alternating current induced in said fieldwinding while said motor operates as an induction motor during starting,switching means operable by said frequency relay, a control relay,having switch contacts and having a coil and having a capacitorconnected in parallel to said coil to accurately select, by capacitortiming, the instant of operation of the relay after the coil andcapacitor are deenergized by the opening of said switching means by theoperation of the frequency relay, the adjustment of the capacitor andthe operating characteristics of the frequency relay as it opens saidswitching means for longer and longer intervals of time as the motorapproaches synchronous speed being so selected that the control relayoperates at an instant when the motor is at a selected per cent ofsynchronous speed, a second control relay similar to the firstcontrolled in its operation by the interconnection efi'ected with saidcontrol circuit by the position of the switch contacts operated by thefirst control relay, the capacitor of the second control relay being soadjusted with reference to the coil of the second control relay that thesecond control relay operates with sufficient delay after the closing ofsaid switch contacts that a given pole of the synchronous motor holds agiven position with reference to a given point on the rotating flux wavein the armature winding, and means operable by the second control relayfor effecting the operation of the field contactor.

2. In a synchronous motor starting control scheme of the type described,the combination of a synchronous motor having an armature, or primary,winding and a field winding, a plurality of terminal leads normallyenergized with alternating current, a pair of terminal leads normallyenergized with direct current, a contactor for connecting the armatureWinding to the terminals energized with alternating current, a fieldcontactor for connecting the field winding to the terminals energizedwith direct current, and a control system for controlling the operationof the field contactor, said control system comprising, an energizedcontrol circuit, a control relay connected to the control circuit andhaving switch contacts to be operated thereby and having a coil and acapacitor of a given selected capacity connected in parallel to the coilto accurately select, by capacitor timing, the instant of operation ofthe relay after the coil and capacitor are deenergized, a frequencyrelay, switching means operable by said frequency relay for deenergizingsaid control relay by operation of said switching means to disconnectsaid control relay from said control circuit, said frequency relay beinginterconnected with the field winding to be energized with thealternating current induced in the field winding while said motor isoperating as an induction motor during starting, the combinedcharacteristics of the control relay and frequency relay being such thatthe control relay functions at an instant when the motor operates at aselected slip, and a second control relay similar to the firstcontrolled in its connection to the control circuit by the switchcontacts and having its capacitor timing so adjusted that the secondcontrol relay will operate with sufficient delay after the opening ofthe switch contacts to thus effect the operation of the field contactorat an instant when the field winding holds a selected angular positionwith reference to the rotating flux in the armature winding.

3. In synchronous motor starting control scheme of the type described,the combination of a synchronous motor having an armature, or primary,winding and a field winding, a plurality of terminal leads normallyenergized with alternating current, a pair of terminal leads normallyenergized with direct current, a contactor for connecting the armaturewinding to the terminals energized with alternating current, a fieldcontactor for connecting the field winding to the terminals energizedwith direct current, and a control system for controlling the operationof the field contactor, said control system comprising, an energizedcontrol circuit, a control relay connected to the control circuit havingswitch contacts operated thereby and having a coil and a capacitor of agiven selected capacity connected in parallel to the coil to accuratelyselect, by capacitor timing, the instant of operation of the relay afterthe coil and capacitor are deenergized, a frequency relay, switchingmeans operable by said frequency relay for deenergizing said controlrelay by operation of said switching means to disconnect said controlrelay'from said control circuit, said frequency relay beinginterconnected with the field Winding to be energized with thealternating current induced in the field winding while said motor isoperating as an induction motor during starting, the combined 0characteristics of the control relay and frequency relay being such thatthe control relay functions at an instant when the motor operates at aselected slip, a set-up relay having a swi; for

connecting the field contactor to the c' trol circuit to thus effect theoperation of ti d contacts-r and a second control relay si to the firstcontrolled 1 its connection to conthe armature winding.

4. In a synchronous motor starti g control scheme of the type described,the combination of rreature, or

a synchronous motor having an primar", winding a hold winding, ofterminal is normally energized "'vlth alternating current, a pair ofterminal leads no ily energized with direct current, a contactor forconnecting the armature winding to the t nals energized with alternatingcurrent, 21, held cont-actor for connecting the field wind ng to theterminals energized with direct c'crre a control system for controllingthe of the field contactor, said control prising, an energized controlcircuit, a control relay connected to the control circu having switchcontacts operated thereby and having a coil and a capacitor of a givenselected capacity connected in parallel to the coil to accuratelyselect, by capacitor timing, the instant of opera tion of the controlrelay after the coil and capacitor deenergized, a frequency relay,switching means operable by the frequency relay whereby said frequencyrelay upon drop-out disconnects the control from the control circuit andthus deenergizes the coil and capacitor of the control relay, saidfrequency relay having a coil, and rectifier connected in seriestherewith, connected to the field winding whereby the coil of thefrequency relay is energized by pulsations of direct c rrent thefrequency of which varies with the per cent slip, the characteristics ofthe control relay and frequency relay combination being so selectedthatthe control relay drops out at a selected low per cent slip, and asecond control relay to the first having its coil and capacitorcontrolled in its connection to the control circuit by the said switchcontacts and having its capacitor timing so adjusted that the secondcontrol relay will operate with a sufficient delay after the opening ofthe switch contacts that the field winding and rotating flux in thearmature winding have a selected angular relation, and means responsiveto the drop-out of the a plural 8 second control relay for effecting theoperation of the field contactor.

5. In a synchronous motor starting control scheme of the type described,the combination of a synchronous motor having an armature, or primary,winding and a field winding, a plurality of terminal leads normallyenergized with alternating current, a pair of terminal leads normallyenergized with direct current, a contactor for connecting the armaturewinding to the terminals energized with alternating current, a fieldcontactor for connecting the field winding to the terminals energizedwith direct current, and a control system for controlling the operationof the field contactor, said control system comprising, an energizedcontrol circuit, a con trol relay connected to the control circuithaving switch contacts operated thereby and having a coil and acapacitor of a given selected capacity connected in parallel to the coilto accurately select, by capacitor timing, the instant of operation ofthe control relay after the coil and capacitor are dcenergized, afrequency relay, switching means operable by the frequency relay wherebysaid frequency relay upon drop-out disconnects the control relay fromthe control circuit and thus deenergizes the coil and capacitor of thecontrol. relay, said frequency relay having a coil, and rectifierconnected in series therewith, connected to the field winding wherebythe coil of the frequency relay is energized by pulsations of directcurrent the frequency of which varies with the per cent slip, thecharacteristics of the control relay and frequency relay combinationbeing so selected that the control relay drops out at a selected low percent slip, and a second con trol relay similar to the first having itscoil and capacitor deenergized by the drop-out and thus the opening ofsaid switch contacts of the first control relay, the capacitor timing ofthe second control relay being so adjusted that the second control relaydrops out with just the right time delay after opening of the switchcontacts that the field Winding and rotating flux in the armaturewinding have a selected angular relation, and means responsive to thedrop-out of the second control relay for effecting the operation of thefield contactor, and a pull-out relay connected to the field winding bythe field contactor, said pull-out relay being energized upon loss ofsynchronism of the motor to reset the system of control to resynchronizethe motor.

EMILIAN M. DAUGE T.

Name Date Heumann et a1. June 28, 1948 Number

